It is known that reinforcing fillers such as carbon black and silica greatly improve the strength and fatigue properties of elastomeric compounds. It is also known that chemical interaction occurs between the elastomer and the filler. For example, good interaction between filler, in particular carbon black and highly unsaturated elastomers such as polybutadiene (BR) and styrene butadiene copolymers (SBR) occurs because of the large number of carbon-carbon double bonds present in these copolymers. Butyl elastomers are known to interact poorly with fillers like carbon black. For example, a compound prepared by mixing carbon black with a combination of BR and butyl elastomers results in domains of BR, which contain most of the carbon black, and butyl domains-which contain very little carbon black. It is also known that butyl compounds have poor abrasion resistance.
WO-99/09036-A1 discloses protected thiol modifiers in general and also their use in silica filled compound comprising organic polymers. However, this reference is silent about the beneficial use of protected thiol modifiers in compounds comprising halogenated butyl rubbers. Butyl elastomers may have only one tenth, or fewer, of the carbon-carbon double bonds found in BR or SBR as disclosed in WO-99/09036-A1. Thus, our findings that the use of protected thiol modifiers in fact results in compounds with a very good balance of physical properties while still maintaining acceptable levels of processability is surprising.